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基于无偏估计的装甲装备器材需求灰色预测 被引量:1
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作者 刘素兵 曹大志 赵志辉 《云南民族大学学报(自然科学版)》 CAS 2019年第5期491-495,共5页
针对装甲装备器材需求数据采集过程中存在的数据采集偏差,建立了存在数据采集误差的装备器材需求灰色预测模型;分析了装备器材需求灰色预测模型中,最小二乘估计为无偏估计的条件是数据采集误差的期望为0,否则,最小二乘估计为有偏估计;... 针对装甲装备器材需求数据采集过程中存在的数据采集偏差,建立了存在数据采集误差的装备器材需求灰色预测模型;分析了装备器材需求灰色预测模型中,最小二乘估计为无偏估计的条件是数据采集误差的期望为0,否则,最小二乘估计为有偏估计;最后针对数据采集偏差期望不为0的条件,给出一种基于辅助变量的无偏参数估计方法.通过实际案例仿真分析验证了方法的合理性和可行性. 展开更多
关键词 装备器材需求 灰色预测 无偏估计 最小二乘法 辅助变量
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n阶行列式的计算方法研究 被引量:3
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作者 刘素兵 郝琳 陈春梅 《赤峰学院学报(自然科学版)》 2019年第2期17-19,共3页
线性代数研究的核心内容之一是线性方程组,行列式是线性代数中重要的内容之一,它是研究线性方程组必不可少的工具,具有举足轻重的作用.然而,对于一些较为复杂的n阶抽象行列式的计算,对于线性代数初学者来说往往十分困惑、难以入手.因此... 线性代数研究的核心内容之一是线性方程组,行列式是线性代数中重要的内容之一,它是研究线性方程组必不可少的工具,具有举足轻重的作用.然而,对于一些较为复杂的n阶抽象行列式的计算,对于线性代数初学者来说往往十分困惑、难以入手.因此,本文讨论了不同类型的n阶行列式,基于行列式的性质,给出其相应的计算技巧和方法,释疑解惑. 展开更多
关键词 行列式 行列式性质 行列式计算
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Contrast sensitivity and higher-order aberrations in patients with astigmatism 被引量:16
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作者 ZHENG Guang-ying DU Jun +7 位作者 ZHANG Jin-song liu su-bing NIE Xiao-li ZHU Xiao-hong TANG Xiu-xia XIN Bao-li MAI Zhi-bin ZHANG Wei-xia 《Chinese Medical Journal》 SCIE CAS CSCD 2007年第10期882-885,共4页
Background Astigmatism is one of the most significant obstacles for achieving satisfactory visual function. This study was to evaluate the influence of astigmatism on contrast sensitivity (CS) and higher-order aberr... Background Astigmatism is one of the most significant obstacles for achieving satisfactory visual function. This study was to evaluate the influence of astigmatism on contrast sensitivity (CS) and higher-order aberrations. Methods CS, accommodation response and wavefront aberration were measured in 113 patients with astigmatism, aged 18-36 years. Both single and binocular visual performance were examined under four lighting conditions: photopia, photopia with glare, scotopia and scotopia with glare respectively. Accommodation response was classified as normal, abnormal and low. The contribution of the power and axis of astigmatism to CS, accommodation response and wavefront aberration was analyzed. Results As the dioptric power of astigmatism increased, the loss of CS spatial frequency changed from high to intermediate, and then to low frequency. CS scores varied at different illuminance levels, descending in the following sequence: photopia, photopia with glare, scotopia, and scotopia with glare. However, the normal accommodation group showed better CS values under photopia with glare than without glare. The range of influenced direction of sine-wave gratings remained mostly at the meridian line of high dioptric power, which would be expanded when optical accommadation attenuated. The patients with symmetrical astigmatism got higher CS scores with binoculus vision than with dominant eye vision, while the patients with asymmetrical astigmatism did this only at scotopia with glare. Among higher-order aberrations, coma aberration, secondary coma aberration and the total higher order aberration were influenced by astigmatism, all of which rising with the power of astigmatism increased. Conclusions Reducing astigmatism might improve the performance of visual function. Not only the power of astigmatism should be cut down, but also the binocular axes should be made symmetrically. 展开更多
关键词 ASTIGMATISM contrast sensitivity higher order aberration
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